Nonhuman animal reproducing pathogenic conditions of spinal and bulbar muscular atrophy and remedy for spinal and bulbar muscular atrophy

ABSTRACT

It is intended to provide a model animal faithfully reproducing the pathogenic conditions of spinal and bulbar muscular atrophy, a method of screening a remedy for polyglutamine disease using the same, and a remedy for spinal and bulbar muscular atrophy. Namely, a nonhuman animal having the following characteristics (1) to (5) in its conditions or pathological findings: (1) showing progressive myoatrophy; (2) showing lowering in muscular power; (3) in immunostaining with the use of an anti-polyglutamine antibody, showing nuclear diffuse staining and nuclear inclusions; (4) in immunostaining with the use of an anti-androgen receptor antibody, showing nuclear diffuse staining and nuclear inclusions; and (5) showing a neurogenic change. A remedy for polyglutamine disease is screened by administering a test substance to this nonhuman animal and examining changes in its conditions or pathological findings. A remedy for spinal and bulbar muscular atrophy is prepared by using as the active ingredient a compound having an effect of inhibiting the secretion of testosterone.

TECHNICAL FIELD

The present invention relates to a non-human animal in which gene modification was performed. More particularly, the present invention relates to a non-human animal showing symptoms and pathologic findings being characteristic of spinal and bulbar muscular atrophy and the use thereof, as well as a therapeutic agent and a treatment method for spinal and bulbar muscular atrophy.

BACKGROUND ART

Spinal and bulbar muscular atrophy (SBMA) is an X-linked recessive and late-onset slow progressive lower motor neuron disease (Sobue et al., 1989; and Kennedy et al., 1968). Major symptoms are lowering of muscular power (weakness) and muscular atrophy in proximal limbs as well as bulbar palsy. Sensory nerve involvement, mainly deep sense impairment, is also found. As concomitant symptoms, gynecomastia is found at high rate, and hepatic dysfunction, glucose tolerance disorder, hyperlipidemia, hypertension, and the like, are often found. Also feminized skin, testicular atrophy, infertility and impotence are sometimes found. Female carriers are usually asymptomatic, although some express tremorof fingers, muscle cramp, mild increase in CK value, etc. (Sobue et al., 1993). A specific treatment for SBMA has not been established. Testosterone may be used as a symptomatic treatment, however, its effect is poor and the efficacy of long-term use has not been confirmed.

Pathologic conditions of SBMA include degeneration, or loss, of neurons in the ventral horn, facial nucleus and hypoglossal nucleus, which is caused by the abnormal expansion of CAG repeat in the first exon of the androgen receptor (AR) (La Spada et al., 1991). Normal number of the CAG repeats in AR gene is about 12 to 34, while that of SBMA patients is expanded to about 40 to 62. Therefore, SBMA is called polyglutamine disease along with Huntington's disease, spinocerebellar ataxias, etc. These diseases share several pathologic conditions such as anticipation and variation in the number of CAG repeats (somatic mosaicism) (Tanaka et al., 1999), selective impairment of neuronal tissue. Furthermore, similar to the other polyglutamine diseases, SBMA also shows a negative correlation between the number of CAG repeats and age at onset of lowering of muscular power, and a positive correlation between the number of CAG repeats and the disease severity adjusted by age (Doyu et al., 1992).

Pathologically, nuclear inclusions stained with an anti-polyglutamine antibody and an anti-androgen receptor antibody are observed in the ventral horn, motor nucleus of lower cranial nerves, kidney, testis, skin, etc. (Li et al., 1998a; and Li et al., 1998b). Nuclear inclusion is among pathological characteristics of polyglutamine diseases and is thought to be involved in pathologic conditions of the disease (Zoghbi and Orr, 2000, and Paulson, 2000). However, the importance of nuclear inclusion in the pathophysiology of polyglutamine diseases has not been established. Some views that nuclear inclusion reflects a cellular protective mechanism for protecting the neuronal cell from the toxicity of the polyglutamine tract. On the other hand, many studies have suggested that, in almost all the polyglutamine diseases, nuclear translocation of mutant protein containing the polyglutamine tract is essential to the development of pathologic conditions (Klement et al., 1998, and Saudou et al., 1998). Unlike other polyglutamine diseases, SBMA is unique in that intracellular distribution of mutant protein changes due to the effect of the specific ligand. That is to say, it is known that AR, that is, a causative protein of SBMA, usually exists in cytoplasm as a complex in an inactivated state, and is transferred into the nucleus when it is bonded to testosterone that is a ligand (Zhou et al., 1994).

A toxic gain of function has been considered the main stream of the pathophysiology in polyQ diseases, but a loss of function of mutant proteins may also play a role (Zoghbi and Orr, 2000, Rubinsztein 2002). Although the expansion of polyQ tract in AR deteriorates the transcriptional activities of AR, and affects its interaction with other transcriptional factors and activators (Mhatre et al., 1993, Kazemi-Esfarjani et al., 1995, Chamberlain et al., 1994, Nakajima et al., 1996), the neurologic impairment in SBMA can not be attributed to the loss of AR function (Maclean et al., 1995, McPhaul et al., 1993), a reason why testosterone shows insufficient and transient effects when used as a therapeutic agent for SBMA (Danek et al., 1994, Goldenberg et al., 1996, Neuschmid-Kaspar et al., 1996).

There have been no substantially effective therapeutic approaches to the polyQ diseases. In a Tg mouse model of HD, expression of a dominant-negative caspase-1 mutant extended survival and delays the appearance of neuronal inclusions (Ona et al., 1999). Inhibition of mutant gene expression demonstrated the reversibility of phenotypic progression in a Tg mouse model of HD (Yamamoto et al., 2000). However, these gene modulations can not be directly applied clinically. Transglutaminase inhibitors suppressed aggregate formation and apoptosis in a cell model of DRPLA (Igarashi et al., 1998) and prolonged survival in a Tg mouse model of HD (Karpuj et al., 2002). An in vitro model of HD showed inhibition of huntingtin fibrillogenesis by specific antibodies and small molecules (Heiser et al., 2000). Creatine increased survival and delayed motor symptoms in a Tg mouse model of HD (Andreassen et al., 2001). Over-expression of molecular chaperone HSP70 demonstrated preventive effects in a Drosophila model of Machado-Joseph disease (Warrick et al., 1999) and SCA1 cell and Tg mouse models (Cummings et al., 1998, Cummings et al., 2001). HSP70 and HSP40 showed preventive effects also in a SBMA cell model (Kobayashi et al., 2000). These and other therapeutic approaches have, yet, remained insufficient or minimal in prevention of phenotypic expression and progression. Recently reported histone deacetylase inhibitors in a Drosophila model could be a promising candidate therapy for polyQ diseases (Steffan et al., 2001), but their therapeutic efficacy should be assessed in a Tg mouse model.

Meanwhile, generation of mouse models of SBMA and development of treatment method using the same have been attempted and some have been reported so far. Since no phenotypes were found in mice including a human androgen receptor gene (AR gene) having 45 or 66 CAG repeats, which are the same level as those of SBMA (Bingham et al., 1995, La Spada et al., 1998, and Merry et al., 1996), a Tg mouse having a truncated AR gene or a strong promoter have been developed for the purpose of obtaining mice showing symptoms. Mice expressing only 239CAG repeats under promoters of AR genes (Adachi et al., 2001) and mice in which a truncated AR gene having 112 CAG repeats is introduced (Abel et al., 2001) showed nuclear inclusions in the spinal motor neuron, in addition to symptoms such as motor weakness, weight loss, short life-span, etc.

As mentioned above, SBMA shows a remarkable sexual difference, that is, most patients are men and even if women have genetic abnormality, symptoms hardly appear. However, in the previous transgenic mice into which a truncated AR gene is introduced, such a sexual difference in symptoms is not observed (Adachi et al., 2001, and Abel et al., 2001). It is thought that no sexual difference in symptoms is found because transgenes of these mice do not have a full length and do not have the sequence encoding a biding site to ligand (testosterone). There was in the past only one SBMA Tg mouse model with a full-length human AR, which showed motor impairment, however, no significant sexual difference in symptoms has not been reported (Morrison et al., 2000).

SUMMARY OF THE INVENTION

The present invention was made on the basis of the above-mentioned background, and the final object of the present invention is to establish a treatment method for polyglutamine diseases (in particular, spinal and bulbar muscular atrophy). A specific problem thereof is to provide a model animal that faithfully reproduces pathologic conditions of human spinal and bulbar muscular atrophy, and to provide a screening method or an assessment method of a therapeutic agent for polyglutamine diseases using the model animal, as well as to provide a therapeutic agent and a treatment method for polyglutamine diseases.

The present inventors have investigated from the viewpoint of the above-mentioned problems, and succeeded in generating a transgenic mouse that faithfully reproduces the pathologic conditions of human spinal and bulbar muscular atrophy (SBMA). That is to say, firstly, the present inventors have attempted to generate a transgenic mouse (Tg mouse) by using a DNA construct containing a human androgen receptor (AR) gene having a CAG repeat sequence having 24 or 97 CAG repeats. When the present inventors have investigated symptoms and pathologic findings of the obtained Tg mouse, a Tg mouse having 97 CAG repeats faithfully reproduced the pathologic conditions of SBMA. In particular, unlike various kinds of SBMA model mice reported conventionally, this mouse model reproduces characteristics of human SBMA, that is, significant sexual difference in symptoms.

Then, various experiments using the Tg mice showed that when castration was performed to male mice so as to reduce the amount of circulating testosterone, symptoms and pathologic findings as shown in SBMA were remarkably improved. On the contrary, it was found that when testosterone was administered to female mice, symptoms, etc. as shown in SBMA were remarkably deteriorated. On the other hand, when an LHRH analog, having an effect of reducing luteinizing hormone-releasing hormone (LHRH) receptors of the pituitary gland, inhibiting the secretion of gonadotropin (LH, FSH, etc.) from the pituitary gland, and thereby inhibiting the secretion of testosterone, was administered to male Tg mice and the effect thereof was observed, similar to the case where the castration was performed, symptoms were remarkably improved. These results provide findings that reducing the circulating testosterone level is an effective means for the treatment of SBMA.

The present invention was completed based on the above results and provides the following configurations.

-   [1] A non-human animal comprising the following characteristics (1)     to (5) in symptoms or pathologic findings:

(1) showing progressive muscular atrophy;

(2) showing lowering in muscular power;

(3) showing diffuse nuclear staining and nuclear inclusions in immunostaining with the use of an anti-polyglutamine antibody;

(4) showing diffuse nuclear staining and nuclear inclusions in immunostaining with the use of an anti-androgen receptor antibody; and

(5) showing neurogenic change.

-   [2] A non-human animal described in [1], wherein when the animals     are females, the above-mentioned (1) to (5) are not found or are     found more slightly or mildly as compared with the case in male     animals. -   [3] A non-human animal described in [1] or [2], wherein the     non-human animal is Rodentia. -   [4] A non-human animal described in [1] or [2], wherein the     non-human animal is a mouse. -   [5] A method of screening therapeutic agents for polyglutamine     diseases, the method comprising the following steps (a) and (b):

(a) administering a test agent to the non-human animal described in any of [1] to [4]; and

(b) examining whether or not at least one of the following (1) to (9) is improved in the non-human animal after the test agent was administered,

-   -   (1) progressive muscular atrophy;     -   (2) lowering in muscular power;     -   (3) an amount of diffuse nuclear staining and nuclear inclusions         found in immunostaining with the use of an anti-polyglutamine         antibody;     -   (4) an amount of diffuse nuclear staining and nuclear inclusions         found in immunostaining with the use of an anti-androgen         receptor antibody;     -   (5) neurogenic change;     -   (6) progressive motor impairment;     -   (7) reduction in body size;     -   (8) short life-span; and     -   (9) reduced activity.

-   [6] A method for screening therapeutic agents for polyglutamine     diseases, the method comprising the following steps (A) and (B):

(A) administering a test agent to the non-human animal described in any of [1] to [4] and to the wild type thereof; and

(B) comparing and assessing the level of at least one of the following (1) to (9) between the administered non-human animal and the wild type,

-   -   (1) progressive muscular atrophy;     -   (2) lowering in muscular power;     -   (3) an amount of diffuse nuclear staining and nuclear inclusions         found in immunostaining with an anti-polyglutamine antibody;     -   (4) an amount of diffuse nuclear staining and nuclear inclusions         found in immunostaining with an anti-androgen receptor antibody;     -   (5) neurogenic change,     -   (6) progressive motor impairment;     -   (7) reduction in body size;     -   (8) short life-span; and     -   (9) reduced activity.

-   [7] The screening method described in [5] or [6], wherein the test     agent is selected from compounds having an effect of inhibiting the     secretion of testosterone.

-   [8] A therapeutic agent for polyglutamine diseases, comprising, as     an active ingredient, the compound selected by the screening method     described in any of [5] to [7].

-   [9] A therapeutic agent for spinal and bulbar muscular atrophy,     comprising, as an active ingredient, a compound having an effect of     inhibiting the secretion of testosterone.

-   [10] A therapeutic agent for spinal and bulbar muscular atrophy,     comprising, as an active ingredient, a compound having an effect of     inhibiting the secretion of gonadotropin from the pituitary gland.

-   [11] A therapeutic agent for spinal and bulbar muscular atrophy,     comprising, as an active ingredient, a compound having an effect of     reducing luteinizing hormone-releasing hormone receptors by acting     on the pituitary gland.

-   [12] A therapeutic agent for spinal and bulbar muscular atrophy,     comprising, as an active ingredient, an analog of luteinizing     hormone-releasing hormone.

-   [13] A therapeutic agent for spinal and bulbar muscular atrophy,     comprising, as an active ingredient, Leuprorelin or the derivative     thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Schematic structure of DNA constructs used in Examples, graph summarizing the results of experiment on symptoms of Tg mice, and graph summarizing the results of experiment on the expression of transgene. A. Schematic view of the transgene constructs. The DNA construct was composed of a cytomegalovirus enhancer (E), a chicken β-actin promoter (Pro), a full-length human AR containing 24 or 97 CAGs (hAR), and a rabbit β-globin polyadenylation signal sequence (polyA). B, C, D and E. Sexual differences in body weight (B, #2-6), rotarod task (C, #7-8), cage activity (D, #2-6), and survival rate (E, #7-8). All parameters are significantly different between the male mice (●, n=8) and female mice (◯, n=8) (p=0.001, p=0.003, p=0.005, and p=0.001, respectively). F. Western blot analysis of total homogenates from the muscle of the male (M) and female (F) mice of AR-97Q, AR-24Q and normal littermates (12-week-old) immunolabeled by an antibody (N-20) against AR. Mouse AR was hardly detectable in the normal littermates. Comparison with muscle extracts from normal littermates indicated that most of the lower bands in transgenic (Tg) mice represent truncated human AR. Protein lysate from Neuro2a cells transfected with the transgene containing 24 CAGs and that with 97 CAGs (AR24 and AR97) are shown for size comparison. G. Western blot analysis of nuclear (N) and cytoplasmic (CY) fractions from the muscle of the male (M) and female (F) AR-97Q mice (#7-8, 14-week-old) immunolabeled by N-20.

FIG. 2. Views summarizing pathologic findings of Tg mice. A. Immunohistochemical study of the male and female AR-97Q mice stained with a monoclonal antibody (1C2) against abnormally expanded polyglutamine (#7-8, 14-week-old). B, C, C, D and E. Electron microscopic immunohistochemistry for 1C2 of an anterior horn cell (#4-6, 24-week-old). Dense granular aggregate of 1C2-immunoreactive material was recognized in the motor neuron nucleus which showed a nuclear inclusion in light micrograph (B, low magnification and C, high magnification). Another motor neuron (D, arrow), which demonstrated diffuse nuclear staining in light micrograph, showed microaggregates in high magnification (E). F. HE staining of the muscle in the male AR-97Q mouse revealed obvious grouped atrophy and small angulated fibers. G. Toluidine blue staining and the histogram of myelinated fiber diameter of the L5 ventral root of male AR-97Q mice and their normal littermates. Large myelinated fibers in the ventral root showed axonal atrophy in the male AR-97Q mice (▪, n=3) compared with normal littermates (□, n=3) (#7-8, 13-week-old).

FIG. 3. Effects of castration on the symptomatic phenotypes of male AR-97Q mice. A, B, C, and D. Body weight (A, #7-8), rotarod task (B, #7-8), cage activity (C, #7-8), and survival rate (D, #2-6) of the castrated (◯, n=6) and sham-operated (●, n=6) male AR-97Q mice. All parameters are significantly different between the sham-operated male AR-97Q mice and the castrated male AR-97Q mice or castrated male littermates (▪, n=2) (p=0.0001, p<0.0001, p=0.006, and p=0.0006, respectively). E. The castrated AR-97Q mouse (E, top) shows no muscular atrophy, which is striking in control mouse (E, bottom) (#2-6, 12-week-old). F. Foot prints of 12-week-old castrated (C) and control (S) male mice (#2-6). Front paws are in red, and hind paws in blue paint.

FIG. 4. Effects of castration on transgene expression and neuropathology of male AR-97Q mice. A. Western blot analysis of total homogenates from the spinal cord and muscle of the castrated (C) and control (S) male AR-97Q mice, that was immunolabeled by N-20 (#7-8, 13-week-old). B. Western blot analysis of nuclear (N) and cytoplasmic (CY) fraction from the muscle of the castrated (C) and control (S) male AR-97Q mice, immunolabeled by N-20 (#7-8, 13-week-old). C. Immunohistochemical study using 1C2 showed marked differences of diffuse nuclear staining and nuclear inclusions between the castrated and sham-operated AR-97Q mice in the spinal anterior horn and the muscle (#7-8, 13-week-old).

FIG. 5. Effects of Leuprorelin on the symptoms of male AR-97Q mice. A, B, C, and D. Body weight (A, #7-8), rotarod task (B, #7-8), cage activity (C, #7-8), and survival rate (D, #7-8) of Leuprorelin-administered and control (vehicle-administered) male AR-97Q mice. All parameters showed significant difference between the Leuprorelin-administered group (●, n=6) and the control group (◯, n=6). The body size of the Leuprorelin-administered group (E, top) was normal, while that of the control group (E, bottom) showed severe muscular atrophy (#4-6, 12-week-old). F. Foot prints of 12-week-old Leuprorelin-administered (L) and control (V) male mice (#4-6). Front paws are in red, and hind paws in blue paint.

FIG. 6. Effects of testosterone on the symptoms of female AR-97Q mice. A, B, C, and D. Body weight (A, #7-8), rotarod task (B, #7-8), cage activity (C, #2-6), and survival rate (D, #7-8) of testosterone-administered and control (oil-administered) female AR-97Q mice. All parameters showed significant difference between the testosterone-administered group (●, n=6) and testosterone-administered normal mice (●, n=4), or the control group (◯, n=6) (p<0.0001). The testosterone-administered AR-97Q mouse (E, top) showed severe muscular atrophy, but the body size of the control group (E, bottom) is normal (#2-6, 14-week-old). F. Foot prints of 14-week-old testosterone-administered (T) and control (O) mice (#2-6). Front paws are in red, and hind paws in blue paint.

FIG. 7. Effects of testosterone on transgene expression and pathologic findings of male AR-97Q mice. A. The results of Western blot analysis of testosterone-administered group (T) and control group (O) using total homogenate of the spinal cord and muscle (#2-6, 12-week-old). N-20 was used as an antibody. B. The results of Western blot analysis of nuclear (N) and cytoplasmic (Cy) fractions from the muscle of the testosterone administered group (T) and control group (O) (#2-6, 12-week-old). N-20 was used as an antibody. Diffuse nuclear staining and nuclear inclusions found in immunostaining of the spinal cord and muscle by using 1C2 showed the remarkable difference between the testosterone-administered group and control group (C).

FIG. 8. Table summarizing the phenotypes of Tg mice generated in Examples. Each datum is expressed by male/female. In table, “−” indicates “not detected,” “+” indicates “mild diffuse nuclear staining and nuclear inclusions are detected,” “++” indicates “severe diffuse nuclear staining and nuclear inclusions are detected” and “ND” indicates “no data,” respectively.

FIG. 9. Table summarizing the results of experiment using 1C2 antibody. In table, “−” indicates “not detected,” “+” indicates “slightly detected,” “++” indicates “moderately detected,” and “+++” indicates “highly detected,” respectively. When the findings are different between lines, the range of level is shown by using “−.” Three lines of mice, #2-6, #4-6 and #7-8, are subjected to pathologic analysis at the age of 12, 18 and 15 week-old, respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

The first aspect of the present invention provides a non-human animal characterized by showing at least the following symptoms and pathologic findings.

The symptoms include (1) progressive muscular atrophy and (2) lowering in muscular power (weakness). Typically, as a result of or in relation to these symptoms, symptoms such as progressive motor impairment, reduction in body size, short life-span, and reduced activity, etc. are also found. Herein, the presence and level of progressive muscular atrophy can be confirmed, for example, by visually observing a certain site such as hind limbs and examining its change over time. On the other hand, the presence or level of lowering in muscular power can be confirmed indirectly from, for example, the presence or level of motor impairment or from the presence or level of reduced activity. Note here that the presence or level of motor impairment can be confirmed by, for example, Rotarod task test (Crawley J N. What's wrong with my mouse. Wiley-Liss, New York, Pp 48-52.), and the presence or level of reduced activity can be confirmed by, for example, Cage activity test (Crawley J N. What's wrong with my mouse. Wiley-Liss, New York, Pp 48-52.), respectively. The other symptoms, that is, reduction in body size and short life-span can be confirmed by macroscopic examination or measurement of body weight for body size reduction and by examination of survival rate for short life-span, respectively.

One of the further features of the non-human animal of the present invention is significant sexual difference in symptoms. That is to say, the above-mentioned symptoms progress severely and rapidly in male mice, while not observed or far less severe in female mice as compared with the case of male mice. The difference in the symptoms related to such sexual difference is a feature specific to spinal and bulbar muscular atrophy. Thus, it can be said that the non-human animal of the present invention is extremely useful as a model animal of spinal and bulbar muscular atrophy because of such features.

In the non-human animal of the present invention, typically, as initial symptoms, muscle atrophy of the trunk and hind limbs is observed. Furthermore, typically, following these initial symptoms, weight loss and lowering in motor function are found.

The pathologic findings found in the non-human animal of the present invention include the following (3) to (5): (3) showing diffuse nuclear staining and nuclear inclusions in immunostaining with the use of an anti-polyglutamine antibody; (4) showing diffuse nuclear staining and nuclear inclusions in immunostaining with the use of an anti-androgen receptor antibody; and (5) showing neurogenic change. Herein, immunostaining can be carried out to the neuronal cell such as the spinal cord, cerebrum, cerebellum, etc. and non-neuronal tissue cells such as the muscle, heart and pancreas, etc. The non-human animal of the present invention shows the presence of such diffuse nuclear staining and nuclear inclusions from the age of about 4-week-old and the amount thereof increases according to aging. Note here that electron microscopic observation shows granular aggregates and fine microaggregates respectively corresponding to the above-mentioned diffuse nuclear staining and nuclear inclusions.

The neurogenic change can be confirmed by, for example, observing HE (hematoxylin-eosin) staining of the muscular tissue. Herein, the neurogenic change typically appears as the occurrence of grouped atrophy and small angulated fibers.

The non-human animal of the present invention shows remarkable sexual difference in pathologic findings as well as in the symptoms mentioned above. That is to say, the pathologic findings mentioned above are remarkably found in male mice, but not in female mice. Typically, neurogenic change, in particular, is not found in female mice.

The non-human animal of the present invention includes Rodentia such as mouse, rat, etc., but is not particularly limited thereto. The non-human animal of the present invention can be generated as a transgenic animal by inserting a certain gene into chromosome at the stage of generation. The method of generating transgenic animals may include a microinjection method of directly introducing DNA into the pronucleus of a fertilized egg, a method using a retrovirus vector, a method using ES cells, and the like. Hereinafter, as the method of generating the non-human animal of the present invention, the microinjection method using mice will be described as a specific example.

In the microinjection method, a fertilized egg is collected from the uterine tube of a female mouse, which was confirmed to be mated, and cultured. After culturing, a desired DNA construct is injected into the pronucleus. As the DNA construct, a sequence (which will be referred to as “transgene”) encoding the full-length of a human androgen receptor (which will be also refereed to as “AR”) containing a large number of CAG repeats is used. Herein, the number of CAG repeats needs to be sufficient for the generated transgenic mice to faithfully reproduce features of SBMA, and it is at least 40, preferably 70 or more, more preferably 80 or more, and yet further preferably 90 or more from the viewpoint that the number of CAG repeats in a SBMA patient is generally 40 or more. It is preferable that the DNA construct to be used includes a promoter sequence capable of efficiently expressing transgene. Examples of such a promoter may include a chicken β-actin promoter, a prion protein promoter, a human AR promoter, a neurofilament L-chain promoter, a L7 promoter, and a cytomegalovirus promoter, and the like.

A fertilized egg, which an injection operation was finished, is transplanted into the uterine tube of a pseudopregnant mouse and the transplanted mouse is cultured for a predetermine time so as to obtain a littermate mouse (F0). In order to confirm that transgene is appropriately introduced in the chromosome of the littermate mouse, DNA is extracted from the tail, etc. of the littermate mouse, and subjected to a PCR method using a primer specific to the transgene or a dot hybridization method, etc.

As mentioned above, the non-human animal of the present invention faithfully reproduces the features of spinal and bulbar muscular atrophy, however, most of the features are shared by polyglutamine diseases. Therefore, it is thought that the non-human animal of the present invention is useful for not only a model of spinal and bulbar muscular atrophy but also a model of a wide range of polyglutamine diseases. Therefore, the second aspect of the present invention provides a screening method of therapeutic agents for polyglutamine diseases using the non-human animal of the present invention.

The screening method of the present invention includes (a) a step of administering a test agent to the non-human animal according to the present invention, and (b) a step of examining whether or not symptoms or pathologic findings, which are characteristic of polyglutamine diseases, are improved in the non-human animal after the test agent was administered. In the step (b), when the improvement of the symptoms, etc. to be examined is found, it is determined that the test agent is a promising candidate of a therapeutic agent for polyglutamine diseases.

Note here that “therapeutic agent for polyglutamine diseases” is used as a term including not only agents to be used for the purpose of improving the symptoms of patients having polyglutamine disease but also agents to be used for the purpose of the prevention for individuals who might develop polyglutamine disease. Furthermore, in the present specification, “polyglutamine disease” is a general name of diseases characterized by the expansion of a CAG repeat in a coding region of the gene and includes Huntington's disease, spinocerebellar ataxias, and spinal and bulbar muscular atrophy, etc. Patients of polyglutamine disease share several pathologic conditions, for example, anticipation, variation in the number of CAG repeats (somatic mosaicism), as well as selective impairment of neuronal tissue.

Examples of administering a test agent in the step (a) may include oral, intravenous, intra-arterial, subcutaneous, intramuscular, intraperitoneal injection, or the like.

Examples of the test agent may include peptide, non-peptide low molecular weight compound, protein, glycoprotein, lipid, glycolipid, sugar, etc. They may be natural compounds or may be synthesized. Besides, extract, culture supernatant, or the like, of human cells or non-human animal cells, etc. may be used as the test agent.

When therapeutic agents for spinal and bulbar muscular atrophy among polyglutamine diseases are screened, it is preferable to select a test agent from compounds having an effect of inhibiting the secretion of testosterone. It is advantageous because efficient screening can be carried out. Examples of such compounds may include a compound having an effect of inhibiting the secretion of gonadotropin from the pituitary gland (for example, a compound having an effect of reducing a luteinizing hormone-releasing hormone receptor by acting on the pituitary gland). Further, a specific example of the test agent may include an analog of luteinizing hormone-releasing hormone or the derivative thereof.

The symptoms or pathologic findings being characteristic of the polyglutamine diseases in the step (b) include, for example, (1) progressive muscular atrophy, (2) lowering in muscular power (weakness), (3) an amount of diffuse nuclear staining and nuclear inclusions found in immunostaining with an anti-polyglutamine antibody, (4) an amount of diffuse nuclear staining and nuclear inclusions found in immunostaining with an anti-androgen receptor antibody, (5) neurogenic change, (6) progressive motor impairment, (7) reduction in body size, (8) short life-span; and (9) reduced activity. In the step (b), the change in at least one of the above (1) to (9) is examined. When a plurality of symptoms, etc. are examined, any symptoms may be combined arbitrarily. For example, combination of (1) and (2), combination of (1), (2) and (3), combination of (1), (2), (3) and (4), combination of (1), (2) and (5), combination of (3), (4) and (9) may be employed. Since it is thought that the efficacy of a test agent is generally enhanced in accordance with the increase of symptoms, etc. to be improved, in the step (b), it is preferable to examine a larger number of symptoms mentioned above. However, a correlation between two symptoms, etc. is found, either symptom, etc. may be examined.

Preferably, in parallel with the administration of the test agent to the non-human animal of the present invention, the test agent is administered to a wild type non-human animal. Thus, after administration, the levels of symptoms, etc. being characteristic of polyglutamine diseases are compared and assessed between both animals. The use of wild type animals as a control for comparison in this way enables easy and precise comparison of the efficacies of the test agent.

The compound selected by the screening method of the present invention can be sufficiently expected to be used as a therapeutic agent for polyglutamine diseases. When the selected compound has a sufficient efficacy with respect to polyglutamine diseases, the intact compound can be used as an active ingredient of the therapeutic agent. On the contrary, when the selected compound does not have a sufficient efficacy, the compound can be used as an active ingredient after the efficacy of the compound is enhanced by providing a chemical modification to the compound. Of course, for the purpose of increasing further efficacy, similar modification may be also provided to the compound having sufficient efficacy.

The third aspect of the present invention relates to an agent for spinal and bulbar muscular atrophy and comprises a compound having an effect of inhibiting the secretion of testosterone. Herein, the effect of inhibiting the secretion of testosterone may be obtained as a result of the administration of the agent of the present invention but the agent of the present invention may not directly have the effect. Therefore, the agent of the present invention may include, for example, a component having an effect of inhibiting the secretion of gonadotropin from the pituitary gland so as to inhibit the release of testosterone by gonadotropin, resulting in reducing the secretion amount of testosterone. Examples of such a component includes a component having an effect of reducing the expression amount luteinizing hormone-releasing hormone (hereinafter, which will be referred to as “LHRH”) receptor by, for example, acting on the pituitary gland. For example, an LHRH analog can reduce the amount of LHRH receptors of the pituitary gland by the continuous stimulation thereof. Therefore, as the active ingredient of the present invention, an LHRH analog can be used. Examples of the LHRH analog may include Leuprorelin, Goserelin, Buserelin, and Nafarelin, etc., but is not limited thereto. Note here that Leuprorelin is sold under the pharmaceutical product name of “LEUPLIN®” (general name of active ingredient: leuprorelin acetate) from Takeda Chemical Industries, Co., Ltd. Similarly, Goserelin is sold under the pharmaceutical product name of “Zoladex®” (general name of the active ingredient: goserelin acetate) from AstraZeneca PLC. Similarly, Buserelin is sold under the pharmaceutical product name of “Suprecur®” (general name of the active ingredient: buserelin acetate) from Aventis Pharma Ltd. Similarly, Nafarelin is sold under the pharmaceutical product name of “Nasanyl®” (general name of the active ingredient: nafarelin acetate) from Monsanto Japan Limited.

Note here that various derivatives to which modification is provided to the LHRH analog may be used as the active ingredient of the present invention as long as the effect of the LHRH analog is not lost (also including the case of enhancing the effect).

The agent of the present invention can be formulated according to the usual methods. In formulation, other pharmaceutically acceptable ingredients (for example, carrier, vehicle, disintegrator, buffer, emulsifier, suspension, soothing agent, stabilizer, preservative, antiseptics, physiological salt solution, and the like) can be contained. An example of the vehicle may include lactose, starch, sorbitol, D-mannitol, sucrose, and the like. An example of the disintegrator may include starch, carboxymethyl cellulose, calcium carbonate, and the like. An example of the buffer may include phosphate, citrate, acetate, and the like. An example of the emulsifier may include gum Arabic, sodium alginate, tragacanth, and the like. An example of the suspension may include glyceryl monostearate, aluminium monostearate, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, sodium lauryl sulfate, and the like. An example of the soothing agent may include benzyl alcohol, chlorobutanol, sorbitol, and the like. An example of the stabilizer may include propylene glycol, diethyline sulfite, ascorbic acid, and the like. An example of the preservative may include phenol, benzalkonium chloride, benzyl alcohol, chlorobutanol, methylparaben, and the like. An example of the antiseptics can include benzalkonium chloride, parahydroxy benzoate, chlorobutanol, and the like.

Formulation forms are not particularly limited and may be formulated in a form of, for example, tablets, powder, fine granules, granules, capsules, syrup, injections, topical preparation, and suppository, and the like.

The thus formulated therapeutic agents of the present invention can be administered to patients by oral administration or parenteral administration (intravenous, intra-arterial, subcutaneous, muscular, intraperitoneal injection, and the like).

A further aspect of the present invention provides a treatment method for spinal and bulbar muscular atrophy with the use of the above-mentioned agents. The treatment method of the present invention includes a step of administering an agent containing, as an active ingredient, a compound having an effect of inhibiting the secretion of testosterone, to the living body. As mentioned above, “a compound having an effect of inhibiting the secretion of testosterone” herein is, for example, a compound having an effect of inhibiting the secretion of gonadotropin from the pituitary gland (for example, a compound acting on the pituitary gland so as to reduce the amount of LHRH receptors). Specific examples may include Leuprorelin, Goserelin, Buserelin, Nafarelin, etc., which are known as LHRH analogs, or the derivatives thereof.

The dosage amount of the agents differs depending upon symptoms, and age, sex, body weight of patients, and the like. The person skilled in the art can determine an appropriate dosage amount properly. For example, when an agent containing Leuprorelin as an active ingredient is used, it can be administrated to an adult subject so that the amount of Leuprorelin is about 1.5 to 4.0 mg/day (for example, 3.0 mg/day or 3.5 mg/day) every four weeks.

EXAMPLES

Each experiment in the below mentioned Examples is carried out by the following method unless otherwise noted.

(Transgene)

We generated DNA constructs including a human AR gene having CAG repeat sequence having 24 repeats (24CAG) or CAG repeat sequence having 97 repeats (97CAG) (SEQ ID NO: 1 and SEQ ID NO: 2 in this order) under the control of a chicken β-actin promoter (see FIG. 1A) as follows. pCAGGS vector (Niwa et al., 1991) was digested by HindIII and ligated after filling in, which generated the new NheI site (pCAGGS-NheI). The full-length human AR fragment harboring 24 or 97 CAGs (Kobayashi et al., 1998) were subcloned into pCAGGS-NheI. By direct DNA sequencing, the presence of 24 and 97 CAG repeat sequences was confirmed in the 5.3 and 5.5kb-inserts respectively.

(Generation and Maintenance of Tg Mice)

The final plasmids with SalI-NheI were digested to remove the AR fragments. We generated Tg mice by microinjection into BDF1 fertilized eggs, and obtained 3 founders with AR-24Q and 5 founders with AR-97Q. These mice were backcrossed to C57BL/6J. We screened mouse tail DNA by PCR for the presence of the transgene using the primers 5′-CTTCTGGCGTGTGACCGGCG-3′ (SEQ ID NO:3) and 5′-TGAGCTTGGCTGAATCTTCC-3′(SEQ ID NO:4) and the confirmation of the CAG repeat size using the primers 5′-CCAGAGCGTGCGCGAAGTG-3′(SEQ ID NO:5) and 5′-TGTGAAGGTTGCTGTTCCTC-3′(SEQ ID NO:6). The transgene copy number in each line was determined by densitometric comparison of Southern blot hybridization intensity of the AR DNA with known standards cutting only one site in the transgene using SacII. For determining CAG repeat size, we electrophoresed the PCR products amplified with a Texas Red-labeled primer on 6% denaturing polyacrylamide gel for 12 hours using a 5500 DNA sequencer (Hitachi, Japan).

(Neurological and Behavioral Testing)

We analyzed rotarod task of mice by an Economex Rotarod (Colombus Instruments, USA) weekly during the light phase of the 12 h light/12 h dark cycle as described previously (Adachi et al., 2001). We performed three trials, and recorded the longest duration on the rod for every mouse. We stopped the timer when the mouse fell from the rod or after an arbitrary limit of 180 seconds.

We measured cage activity while each mouse was in a transparent acrylic cage (16×30×14 cm). We used an AB system (Neuroscience, Japan) with an infrared ray sensor monitor to measure spontaneous motor activity. We automatically totaled and recorded all measurements for 24 hours per week at 10-min intervals.

(Hormonal Intervention and Serum Testosterone Assay)

Male AR-97Q mice and their normal littermates were castrated or sham-operated via the abdominal route under ketamine-xylazine anesthesia (50 mg/kg ketamine and 10 mg/kg xylazine, i.p.) at 4 weeks of age. Female AR-97Q mice and their littermates were subcutaneously injected 20 μg of testosterone enanthate dissolved in 20 μl of sesame oil weekly from 4 weeks of age until the end of the analysis. The control mice were given the same amount of sesame oil.

We used Coat-A-Count Total Testosterone radioimmunoassay (Diagnostic Products Corporation, USA) for assaying the serum testosterone levels.

(RNA and Protein Expression Analysis)

We exsanguinated mice under ketamine-xylazine anesthesia, snap-froze their tissues with powdered CO2 in acetone, extracted total RNA from tissues with Trizol (Life Technologies/Gibco BRL, USA), and reverse transcribed the RNA using SUPERSCRIPT II reverse transcriptase (Life Technologies/Gibco BRL). We used 5′-TTCCACACCCAGTGAAGC-3′ (SEQ ID NO:7) and 5′-GGCATTGGCCACACCAAGCC-3′ (SEQ ID NO:8) as primers for specific transgene RNA detection. After amplification, the products were separated by agarose gel electrophoresis. We compared the intensity of the PCR products signals with those of β-actin mRNA levels, which were separately amplified, by ethidium bromide staining.

Frozen tissue (0.1 g wet weight) was homogenized in 1000 μl of 50 mM Tris pH 8.0, 150 mM NaCl, 1% NP-40, 0.5% deoxycholate, 0.1% SDS, and 1 mM 2-mercaptoethanol with 1 mM PMSF and aprotinine at 6 μg/ml (2500 g for 15 min at 4° C). Each lane on a 5-20% SDS-PAGE gel was loaded with protein 200 μg for nervous tissue, and 80 μg for muscular tissue from the supernatant fraction, which was transferred to Hybond-P membranes (Amersham Pharmacia Biotech, England), using 25 mM Tris, 192 mM glycine, 0.1% SDS, and 10% methanol as transfer buffer. After immunoprobing with rabbit anti-AR antibody N-20 (1:1000) (Santa Cruz Biotechnology, USA), we performed second antibody probing and detection using the ECL+plus kit (Amersham Pharmacia Biotech). Nuclear and cytoplasmic fractions were extracted with NE-PER nuclear and cytoplasmic extraction reagents (Pierce, USA).

(Immunohistochemistry)

We perfused 20 ml of a 4% paraformaldehyde fixative in phosphate buffer (pH 7.4) through the left cardiac ventricle of mice deeply anesthetized with ketamine-xylazine, postfixed tissues overnight in 10% phosphate-buffered formalin, and processed tissues for paraffin embedding. Then we deparaffinized 4-μm-thick tissue sections, dehydrated with alcohol, treated in formic acid for 5 minutes at room temperature, and stained with 1C2 (1:10000) (Chemicon, USA), as described before (Adachi et al., 2001). That is to say, after treatment in formic acid, 5% equine serum was reacted at room temperature for 30 min, primary antibody 1C2 (1:10000) (Chemicon, USA) was reacted at 4° C. over night, followed by immunostaining by the ABC method. In the staining by the ABC method, a biotinylated secondary antibody (Vector Laboratories, USA) was reacted at 4° C. over night, washed with 0.02M PBS, reacted with HRP labeled streptavidin, and colored with DAB.

For electron microscopic immunohistochemistry, we used paraffin-embedded tissue sections immunostained with 1C2 (1:10000) (Chemicon) as described previously (Adachi et al., 2001).

(Muscle Histology and Morphometric Analysis of Spinal Motor Neurons and Ventral Spinal Roots)

Six-μm-thick cryostat sections of the gastrocnemius muscles were air dried and stained with hematoxylin and eosin (H & E). For assessment of the neuronal populations and cross-sectional area of the anterior horn cells, 20 serial 5-μm-thick sections from the fifth lumbar spinal cords of 3 mice of each group (#7-8, 13-week-old) were prepared. Every other section was stained by the Nissl technique and all neurons with an obvious nucleolus, present in the anterior horn, were assessed using a Luzex FS image analyzer (Nireco, Japan) as described before (Terao et al., 1996). That is to say, the cross-sectional areas of total 10 sections of the entire neuron were measured. The diameter of myelinated fibers in the ventral spinal roots was measured on the transverse sections stained with toluidine blue as described before (Terao et al., 1996). That is to say, the cross-sectional area of each fiber was measured and the diameter of a circle having the same area was calculated.

(Statistical Analysis)

We analyzed data using the unpaired t-test and denoted p values of 0.05 or less as statistical significance.

Example 1 Generation of Transgenic Mice (Tg Mice) Expressing AR Gene Having 97CAGs and Investigation of Symptoms, etc. of the Obtained Tg Mice

We attempted to generate Tg mice expressing the full-length human AR containing 24 or 97 CAGs under the control of a cytomegalovirus enhancer and a chicken β-actin promoter (FIG. 1A). We established 3 lines with 24 glutamines (AR-24Q) and 5 lines with 97 glutamines (AR-97Q). Copy number of the transgene was 1 to 5 in AR-24Q mice, and 1 to 3 in AR-97Q mice (FIG. 8). We assessed the 24 or 97 CAG repeat in the transgene by the PCR amplification and the on the polyacrylamide gel electrophoresis. The results did not show unequivocal intergenerational instability in the CAG repeat number (data not shown).

Three of 5 lines with AR-97Q (#2-6, #4-6, #7-8) exhibited progressive motor impairment, although no lines with AR-24Q showed any manifested phenotypes. All 3 symptomatic lines showed reduction in body size, short life-span, progressive muscle atrophy and weakness as well as reduced cage activity; all of which were markedly pronounced and accelerated in the male AR-97Q mice, but not observed or far less severe in the female AR-97Q mice regardless of the line (FIGS. 1B, C, D and E). The first detectable phenotype is muscle atrophy of the trunk and hind limbs followed by weight loss and impairment of the rotarod task. We detected the onset of motor impairment by the rotarod task at 8 to 9 weeks of age in the male AR-97Q mice, while 16 weeks or more in the females (FIG. 8). The affected mice were hypoactive and dragged their hind limbs. The forelimbs were not involved until hind limb atrophy became severe. Males showed a markedly faster and earlier motor deficit than females, and shorter lifespan. The 50% mortality ranged from 66 to 135 days of age in the male AR-97Q mice of 3 lines, whereas mortality of the female AR-97Q mice remained only 10 to 30% at more than 210 days in the 3 lines. The cause of death was cachexia due to hyponutrition and dehydration.

Then, we examined the expression of transgene by the detection of protein by Western blot analysis and the detection of mRNA using RT-PCR method. As a result, Western blot analysis showed high expression of mutant AR, including mutant AR in the stacking gel and truncated mutant AR in addition to the mutant monomeric AR band. We detected these proteins in the spinal cord, cerebrum, heart, muscle and pancreas. Although the male mice had more protein within the stacking gel than the female mice, the female mice had more monomeric AR protein (FIG. 1F). AR-24Q mice showed a single band of AR with 24 glutamines without protein in the stacking gel (FIG. 1F). The nuclear fraction contained the most transgene protein within the stacking gel (FIG. 1G). There was no significant difference in the expression of the mRNA of the transgene between the male and female mice. These observations indicate that the nuclear localization is the major expression profile of the transgene protein in the stacking gel. This nuclear localization was more prominent in males than in females, while the mRNA expression levels were indistinguishable between genders.

On the other hand, we performed histological study including immunohistochemistry, as well as muscle histology and morphometric analysis of ventral horn cell and ventral root for each Tg mouse. AR-24Q mice showed no pathologic abnormalities. In AR-97Q mice, we detected diffuse nuclear staining and less frequent NIs with 1C2, an antibody specifically recognizing the expanded polyQ (Trottier et al., 1995), in the neurons of the spinal cord, cerebrum, cerebellum, brain stem and dorsal root ganglia as well as non-neuronal tissue such as the heart, muscle and pancreas (FIG. 9). In the neuronal tissues, the nuclei of the motor neurons showed the most prominent diffuse nuclear staining and NIs. Glial cells also showed marked staining but not the dorsal root ganglia. The regions with diffuse nuclear staining and NIs also showed immunoreactivity to an antibody to AR (N-20). Neither 1C2 nor N-20 revealed immunoreactivity in the cytoplasm. Diffuse nuclear staining and NIs were found at 4 weeks of age and became more profound with aging, although male mice showed markedly abundant diffuse nuclear staining and NIs than females in agreement with the symptomatic and western blot profile differences with gender (FIG. 9, FIG. 2A). Electron microscopic immunohistochemistry for 1C2 demonstrated granular aggregates corresponding to NIs and fine microaggregates corresponding to diffuse nuclear staining in the neuronal tissues (FIGS. 2B, C, D and E).

Muscle histology revealed significant grouped atrophy and small angulated fibers in the male AR-97Q mice as well as mild myopathic change such as increased variability in muscle fiber size (FIG. 2F). Although the number of spinal motor neurons tended to be reduced in AR-97Q mice, the difference was not significant; 452±10/10 sections in L5 segment of AR-97Q mice, and 543±28/10 sections in their littermates (p=0.10). Nevertheless, the cross-sectional area of the individual spinal motor neurons significantly decreased in the male AR-97Q mice; 195.6±12.1 μm² in L5 of male AR-97Q and 130.6±4.0 μm² in their male littermates (p=0.006). In addition, the diameter of large myelinated fibers (=6.0 μm) was significantly diminished in the male AR-97Q mice; the diameter of large fibers of the L5 ventral root was 8.49±0.27 μm in male AR-97Q and 10.29±1.08 μm in their male littermates (p=0.05), whereas that of small fibers (<6.0 μm) was 3.11±0.23 μm in male AR-97Q and 2.86±0.11 μm in their male littermates (p=0.16). Female mice showed no neurogenic changes. Neuronal cell population in the cerebrum, cerebellum and dorsal root ganglia was fairly well preserved despite the abundant diffuse nuclear staining and NIs.

Example 2 Treatment of Male AR-97Q Mice by Castration

We hypothesized that sexual difference in symptoms and pathologic findings is caused by sexual difference of the secretion of testosterone that is androgen. Firstly, we performed castration treatment to male AR-97Q mice. Castrated male AR-97Q mice showed marked improvement of symptoms, pathologic findings, and nuclear localization of the mutant AR compared with control mice (the sham-operated male AR-97Q mice). These castrated male AR-97Q mice weighed the same as their castrated male littermates, whereas the sham-operated male AR-97Q mice showed progressive emaciation (FIG. 3A). Motor impairment assessed by rotarod and cage activity was significantly less or virtually absent in the castrated male AR-97Q mice as compared with control mice (FIGS. 3B and C). The castrated male AR-97Q mice showed motor impairment similar to that of the female AR-97Q mice. The life-span was also significantly prolonged in the castrated male AR-97Q mice (FIG. 3D). The castrated AR-97Q mice showed amelioration of muscle atrophy and reduction in body size (FIG. 3E). In a foot print analysis, the sham-operated male AR-97Q mice exhibited motor weakness with dragging of their hind legs, which improved in the castrated male AR-97Q mice (FIG. 3F). In the western blot analysis using N-20, the mutant AR appearing within the stacking gel was markedly diminished in the castrated male AR-97Q mice compared with the sham-operated male AR-97Q mice (FIG. 4A). The mutant AR in the nuclear fraction also significantly decreased in the castrated male AR-97Q mice (FIG. 4B). The castrated male AR-97Q mice showed markedly diminished diffuse nuclear staining and NIs (FIG. 4C). These observations suggested that castration markedly prevented nuclear localization of the mutant AR protein. The serum testosterone in the castrated male AR-97Q mice dramatically decreased to an undetectable low level, whereas that in sham-operated male AR-97Q mice was 27.7±1.2 ng/dl (#7-8, n=4).

Castration remarkably improved the phenotypes, i.e., symptoms and pathologic findings of male AR-97Q mice. Western blot analysis and 1C2 immunostaining revealed that castration drastically reduced the mutant ARs localized in nucleus. It was confirmed that castration reduced serum testosterone level. Since the nuclear translocation of AR is solely dependent on testosterone (Stenoien et al., 1999, and Simeoni et al., 2000), the reason why the castration shows the treatment effect in male mice is thought to be because castration prevented the nuclear localization of the mutant AR. The nuclear translocation of mutant protein having abnormally expanded polyglutamine is an important factor associated with neuronal dysfunction or degeneration in most of polyglutamine diseases. As one example, The nuclear localization of the mutant protein with expanded polyQ is important in inducing neuronal cell dysfunction and degeneration in the majority of polyQ diseases. Addition of a nuclear export signal to the mutant huntingtin eliminates aggregate formation and cell death in cell models of HD (Saudou et al., 1998, Peters et al., 1999), and a nuclear localization signal had the opposite effect (Peters et al., 1999). In Tg mice of SCA1 having a mutated nuclear localization signal, ataxin-1 was distributed in the cytoplasm, and the mice did not show any neurologic disorders (Klement et al., 1998). In considering such reports, it is thought that the nuclear translocation of mutant AR is prevented by reducing testosterone, which may lead to the improvement of symptoms of SBMA. Such endocrinologic intervention is thought to be sufficiently applicable to treatment of human.

The castrated AR-97Q mice showed phenotypes similar to those of the female AR-97Q mice, implying that motor impairment of SBMA patients can be rescued to the level in female carriers. Almost half of the human SBMA female carriers show mild subclinical electromyographic abnormalities, while few manifest clinical phenotypes (Sobue et al., 1993, Mariotti et al., 2000). Indeed lower expression level of mutant AR in female carriers due to X-inactivation may cause the escape from the manifestation, but our present study also suggests that the low level of testosterone prevents the nuclear localization of the expressed mutant AR, resulting in a lack of phenotypic manifestations in the female carriers.

Example 3 Administration of Leuprorelin to Male AR-97Q Mice

Then, we performed an experiment of administrating Lueprorelin, which is an LHRH analog, to male AR-97Q mice for the purpose of reproducing the treatment of mice by inhibiting the secretion of testosterone by the use of an agent. Leuprorelin was administrated as follows. 100 μg of Leuprorelin acetate was suspended in a solution containing D-mannitol, which was subcutaneously injected to the mice every two weeks from five weeks of age until the end of the analysis. To the control group, only suspension was administrated. The Leuprorelin-administered male AR-97Q mice showed remarkable improvement in symptoms as in castrated mice. That is to say, motor impairment assessed by rotarod and cage activity was far milder in the Leuprorelin-administrated male AR-97Q mice as compared with the control group, and motor dysfunction was hardly shown in the Leuprorelin-administrated group (FIGS. 5A, B, C and D). In Leuprorelin-administrated male AR-97Q mice, reduction in body size was remarkably improved (FIG. 5E) and also motor weakness was improved (FIG. 5F). Serum testosterone value of the Leuprorelin-administrated male AR-97Q mice was undetectable low level (#4-6, n=4).

Leuprorelin is an LHRH analog and is an agent that continuously stimulates the pituitary gland, thereby downregulating the LHRH receptor of the pituitary gland and inhibiting the secretion of LH or FSH from the pituitary gland so as to inhibit the secretion of testosterone. Leuprorelin shows the same level of effect of inhibiting the secretion of testosterone as that by castration (The Leuproride Study Group 1984), substitutes for highly invasive castration and becomes a representative agent for hormone treatment of prostate cancer. Furthermore, its long-lasting effect was confirmed and further the recovery of the secretion of testosterone by stopping the use was also confirmed (Hall et al., 1999). Also from the ethical viewpoint, this agent is suitable for clinical application. In the treatment of SBMA patients, administration of LHRH analog is thought to be more practical as compared with castration that is highly invasive and irreversible treatment. Also in AR-97Q mice, the effect of inhibiting the secretion of testosterone by Leuprorelin is obvious, and the treatment effect was shown also for neurologic impairment by polyglutamine. That is to say, LHRH analog is thought to be the most promising agent as a therapeutic agent for SBMA.

Example 4 Administration of Testosterone to Female AR-97Q Mice

Then, in order to clarify that the treatment effect of castration in male AR-97Q mice is obtained by inhibiting the secretion of testosterone, we performed an experiment of administrating testosterone to female AR-97Q mice, which had originally shown less symptoms. Testosterone administration drastically exacerbated symptoms, pathologic findings and nuclear localization of the mutant protein in the female AR-97Q mice as compared with the control group (sesame-oil administrated group). That is to say, the control group hardly showed weight loss, while the testosterone-administrated mice showed significant weight loss (FIG. 6A). The motor impairment assessed by rotarod and cage activity was significantly worsened in the female AR-97Q mice administered testosterone compared with control mice, being similar to those of the untreated male AR-97Q mice (FIGS. 6B and C). The life-span of the female AR-97Q mice was also affected by testosterone administration (FIG. 6D). The testosterone-administered AR-97Q mice showed marked muscle atrophy and reduction in body size (FIG. 6E). In a foot print analysis, the testosterone-administered female AR-97Q mice exhibited motor weakness and dragged their hind legs, which was not detected in the sesame oil-administered female AR-97Q mice (FIG. 6F). Western blot analysis using N-20 revealed the mutant AR in the stacking gel in whole tissue homogenates as well as in the nuclear fraction, which was larger in amount in the testosterone-administered female AR-97Q mice than in control mice (FIGS. 7A and 7B). The testosterone-administered female AR-97Q mice demonstrated markedly pronounced diffuse nuclear staining and NIs with 1C2 compared with control mice (FIG. 7C). The testosterone-administered female 97Q mice showed markedly higher serum testosterone levels (158.0±70.7 ng/dl in #2-6, n=3; 305.3±182.3 ng/dl in #7-8, n=4) than those in control mice, all of which showed undetectable low level.

As is apparent from the above-mentioned results, administration of testosterone markedly exacerbated symptoms in the female AR-97Q mice, which had been negligible without testosterone treatment. Western blot analysis or 1C2 immunostaining revealed that the administration of testosterone markedly increased mutant AR localized in nucleus. It was confirmed that the administration of testosterone increased the serum testosterone level. Since the nuclear translocation of AR is solely dependent on testosterone (Stenoien et al., 1999, and Simeoni et al., 2000), testosterone may show toxic effects in the female AR-97Q mice by accelerating nuclear translocation of the mutant AR.

As shown in each Example, our Tg mice with the full-length human AR containing 97 CAGs demonstrated progressive motor impairment and neuropathologic changes equivalent to human SBMA. Western blot analysis showed truncated fragments of mutant AR in the affected tissues. These fragments may contribute to pathophysiology in our Tg mice, since several studies have suggested that proteolytic cleavage of mutant protein plays an important role in the pathogenic mechanisms of SBMA as well as other polyQ diseases (Li et al., 1998b, Kobayashi et al., 1998, Wellington et al., 1998, Mende-Mueller et al. 2001). Electron microscopic immunohistochemistry for 1C2 demonstrated granular aggregates and fine microaggregates, which indicates variable stages of pathologic change in the nucleus of motor neurons. Granular aggregate has also been reported in the pathologic study of SBMA (Li et al., 1998b). In AR-97Q mice in Examples, neurogenic changes were evident in muscle pathology, and anterior horn cells and their axons showed significant decrease in size without substantial neuronal loss. These findings indicate that the main pathologic features of our AR-97Q mice was neuronal dysfunction rather than degeneration of the spinal motor neurons, which was also demonstrated in a number of Tg mouse models of other polyQ diseases (Zoghbi and Orr, 2000, Rubinsztein, 2002). All symptomatic mice with AR-97Q showed motor impairment by 21 weeks of age, until when no lines with AR-24Q demonstrated symptoms in spite of the high revel expression of mutant AR protein. Nuclear inclusions and diffuse nuclear staining with 1C2 were found since 4 weeks of age even in female AR-97Q mice, although they are far less frequent than male AR-97Q mice. Nevertheless pathologic studies showed no abnormalities in AR-24Q mice at 12 weeks of age. These findings clarify that the symptomatic and pathologic phenotypes in AR-97Q were not due to overexpression of human AR but due to expanded polyglutamine tract. Moreover, no phenotypes were found in previous SBMA Tg mice with full length human AR despite good transgene expression levels, presumably because the CAG repeat was not long enough (Bingham et al, 1995, La Spada et al., 1998). In other words, the AR-97Q mouse faithfully reproduces pathologic conditions of SBMA and is thought to be an extremely excellent animal model of not only SBMA but also polyglutamine diseases.

The symptoms, pathologic findings and nuclear localization of the mutant AR protein showed a remarkable sexual difference in our AR-97Q mice, and were significantly modified by hormonal intervention either by castration, or Leuprorelin or testosterone administration. Although androgen has been shown to upregulate the expression of AR (Syms et al 1985, Kemppainen et al 1992, Zhou et al 1995), RT-PCR did not reveal any significant sexual difference in the mRNA levels of the transgenic AR gene in our Tg mice, in which the transgene was not controlled by its own promoter with androgen responsive element but by chicken β-actin promoter. That is to say, the mechanism that the testosterone level plays important roles in the sexual difference in symptoms is thought to be not changing the transcription of AR but modifying AR in the post-transcriptional stage, i.e., in the protein level.

Unlike SBMA, in the other polyglutamine diseases, specific ligand of the causative protein has not been found. The drastic effect of treatment by castration of Tg mice in the above-mentioned Examples suggests that polyglutamine diseases can be treated by inhibiting the nuclear translocation of mutant protein.

The present invention is not limited to the description of the above embodiments. A variety of modifications, which are within the scopes of the following claims and which are achieved easily by a person skilled in the art, are included in the present invention.

Document cited in the present description will listed below.

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Hereinafter, the following matters are disclosed.

-   11. A non-human animal comprising the following (1) to (9) in     symptoms or pathologic findings:

(1) progressive muscular atrophy;

(2) lowering in muscular power;

(3) an amount of diffuse nuclear staining and nuclear inclusions found in immunostaining with an anti-polyglutamine antibody;

(4) an amount of diffuse nuclear staining and nuclear inclusions found in immunostaining with an anti-androgen receptor antibody;

(5) neurogenic change, (6) progressive motor impairment;

(7) reduction in body size;

(8) short life-span; and

(9) reduced activity.

-   12. The non-human animal described in 11, wherein the motor     impairment develops at the age of about 8 to 9 weeks. -   13. The non-human animal described in 11 or 12, wherein when the     animals are females, the above-mentioned (1) to (9) are not found or     are formed more mildly or slightly as compared with the case of male     animals. -   14. The non-human animal described in any of 11 to 13, wherein the     non-human animal is Rodentia. -   15. The non-human animal described in any of 11 to 13, wherein the     non-human animal is mouse. -   21. A treatment method for spinal and bulbar muscular atrophy,     comprising the following step (i):

(i) administrating an agent containing, as an active ingredient, a compound having an effect of inhibiting the secretion of testosterone.

-   22. The treatment method described in 21, wherein the compound has     an effect of inhibiting the secretion of gonadotropin from the     pituitary gland. -   23. The treatment method described in 21, wherein the compound has     an effect of reducing luteinizing hormone-releasing hormone     receptors by acting on the pituitary gland. -   24. The treatment method described in 21, wherein the compound is an     analog of luteinizing hormone-releasing hormone. -   25. The treatment method described in 21, wherein the compound is     Leuprorelin or the derivative thereof. -   31. A use of a compound for producing a therapeutic agent for spinal     and bulbar muscular atrophy, the compound having an effect of     inhibiting the secretion of testosterone. -   32. A use of a compound for producing a therapeutic agent for spinal     and bulbar muscular atrophy, the compound having an effect of     inhibiting the secretion of gonadotropin from the pituitary gland. -   33. A use of a compound for producing a therapeutic agent for spinal     and bulbar muscular atrophy, the compound having an effect of     reducing luteinizing hormone-releasing hormone receptor by acting on     the pituitary gland. -   34. A use of analog of luteinizing hormone-releasing hormone for     producing a therapeutic agent for spinal and bulbar muscular     atrophy. -   35. A use of Leuprorelin or the derivative thereof for producing a     therapeutic agent for spinal and bulbar muscular atrophy.

INDUSTRIAL APPLICABILITY

The non-human animal of the present invention faithfully reproduces pathologic conditions of spinal and bulbar muscular atrophy (SBMA) and can be used as a model of SBMA for developing therapeutic agents and for elucidating the causative mechanism of SBMA, etc. Furthermore, the non-human animal of the present invention shows pathologic conditions shared by polyglutamine diseases, so that the animal can be used for developing therapeutic agents not only for SBMA but also for a wide range of polyglutamine diseases.

On the other hand, since the therapeutic agent of the present invention was formulated based on the development mechanism of SBMA and the effect was demonstrated in a model animal that faithfully reproduces pathologic conditions of SBMA, the agent is thought to be extremely useful as a therapeutic agent for SBMA. 

1. A non-human animal comprising the following characteristics (1) to (5) in symptoms or pathologic findings: (1) showing progressive muscular atrophy; (2) showing lowering in muscular power; (3) showing diffuse nuclear staining and nuclear inclusions in immunostaining with the use of an anti-polyglutamine antibody; (4) showing diffuse nuclear staining and nuclear inclusions in immunostaining with the use of an anti-androgen receptor antibody; and (5) showing neurogenic change.
 2. A non-human animal according to claim 1, wherein when the animals are females, the (1) to (5) are not found or are found more slightly or mildly as compared with the case in male animals.
 3. A non-human animal according to claim 1, wherein the non-human animal is Rodentia.
 4. A non-human animal according to claim 1, wherein the non-human animal is a mouse.
 5. A method of screening therapeutic agents for polyglutamine diseases, the method comprising the following steps (a) and (b): (a) administering a test agent to the non-human animal according to claim 1; and (b) examining whether or not at least one of the following (1) to (9) is improved in the non-human animal after the test agent was administered, (1) progressive muscular atrophy; (2) lowering in muscular power; (3) an amount of diffuse nuclear staining and nuclear inclusions found in immunostaining with the use of an anti-polyglutamine antibody; (4) an amount of diffuse nuclear staining and nuclear inclusions found in immunostaining with the use of an anti-androgen receptor antibody; (5) neurogenic change; (6) progressive motor impairment; (7) reduction in body size; (8) short life-span; and (9) reduced activity.
 6. A method for screening therapeutic agents for polyglutamine diseases, the method comprising the following steps (A) and (B): (A) administering a test agent to the non-human animal according to claim 1 and to the wild type thereof; and (B) comparing and assessing the level of at least one of the following (1) to (9) between the administered non-human animal and the wild type, (1) progressive muscular atrophy; (2) lowering in muscular power; (3) an amount of diffuse nuclear staining and nuclear inclusions found in immunostaining with an anti-polyglutamine antibody; (4) an amount of diffuse nuclear staining and nuclear inclusions found in immunostaining with an anti-androgen receptor antibody; (5) neurogenic change, (6) progressive motor impairment; (7) reduction in body size; (8) short life-span; and (9) reduced activity.
 7. The screening method according to claim 5, wherein the test agent is selected from compounds having an effect of inhibiting the secretion of testosterone.
 8. A therapeutic agent for polyglutamine diseases, comprising, as an active ingredient, the compound selected by the screening method according to claim
 5. 9. A therapeutic agent for spinal and bulbar muscular atrophy, comprising, as an active ingredient, a compound having an effect of inhibiting the secretion of testosterone.
 10. A therapeutic agent for spinal and bulbar muscular atrophy, comprising, as an active ingredient, a compound having an effect of inhibiting the secretion of gonadotropin from the pituitary gland.
 11. A therapeutic agent for spinal and bulbar muscular atrophy, comprising, as an active ingredient, a compound having an effect of reducing luteinizing hormone-releasing hormone receptors by acting on the pituitary gland.
 12. A therapeutic agent for spinal and bulbar muscular atrophy, comprising, as an active ingredient, an analog of luteinizing hormone-releasing hormone.
 13. A therapeutic agent for spinal and bulbar muscular atrophy, comprising, as an active ingredient, Leuprorelin or the derivative thereof. 